1. Field of the Invention
This invention relates to a process and apparatus for the treatment of effluents produced by metalorganic chemical vapor deposition (MOCVD).
2. Description of the Related Art
One of the fastest growing semiconductor markets is the compound semiconductor market. The products in this market include devices formed from III-V compositions, such as light emitting diodes (LEDs), high temperature semiconductors and high frequency semiconductors for telecommunications devices.
The III-V compound semiconductors include as the xe2x80x9cIIIxe2x80x9d constituent one or more of the metals or semimetals in Group III of the Periodic Table, such as Al, Ga, or In. The xe2x80x9cVxe2x80x9d constituent of such compound semiconductors is constituted by one or more of the non-metals in Group V of the Periodic Table, such as P or As.
The most widely used manufacturing method for forming III-V compound semiconductors is metal organic chemical vapor deposition (MOCVD). Typical sources for Group V elements include, but are not limited to, arsine (AsH3), phosphine (PH3), tertiary-butyl arsine (TBA), and tertiary-butyl phosphine (TBP), all gaseous materials.
In a typical MOCVD recipe for forming a III-V compound semiconductor, the arsine and phosphine, and/or TBA and TBP, pass into the reactor along with large flows of hydrogen. An estimated 70-95% of arsine and 30-50% of phosphine is destroyed in the MOCVD processing tool, with the As and P depositing on the semiconductor wafer. The remainder of the unreacted arsine and phosphine passes through the tool and then through the pumping system at the exit of the tool, where it is mixed with ballast nitrogen from the pump. Table 1 below shows the components and constituent flows of the gases entering a typical MOCVD tool.
The corresponding components and constituent flows of the gases discharged from the tool and post-pump system are set out in Table 2 below.
The foregoing Table 1 and Table 2 gas components, flow rates and concentration are illustrative, with actual composition of the post-pump effluent in a specific process system being highly dependent on the operating conditions, including the recipe conditions and the efficiency of the tool. In general, however, the concentrations of arsine and phosphine exiting the tool are significantly higher than the threshold limit values (TLVs) of these gases. The TLV for arsine is 50 ppb while the TLV for phosphine is 300 ppb. It therefore becomes necessary to abate the arsine and phosphine exiting the tool.
Effluents that contain arsine and phosphine, typically referred to as hydrides, from MOCVD processes have been successfully abated with dry scrubbers. These dry scrubbers conventionally comprise a mixture of metal oxides. The oxides, usually in the form of a powder, are combined with a small amount of binder material to yield a formable material that can then be extruded, pelletized, or otherwise formed into a small shape to enhance the total surface area and the mass transfer coefficient of the material. These shaped materials are then placed, in bulk, into a container where they are used for the abatement of hydrides.
The chemistry involved in the abatement of the effluent by metal oxides (MOs), where the hydride is arsine (As), is as follows:
3MO+2AsH3xe2x86x92M3As+As+3H2O+heat
Phosphine (PH3) undergoes a similar reaction with metal oxides:
3MO+2PH3xe2x86x92M3P+P+3H2O+heat
Various metal oxides have been found to react in such a manner. These metal oxides include, but are not limited to, oxides of transition metals such as copper oxide, zinc oxide, silver oxide, cobalt oxide, iron oxide, nickel oxide, manganese oxide, and molybdenum oxide.
Metal oxide dry scrubbers have been proven to work well in the abatement of hydrides in the effluent of MOCVD tools, but there are accompanying deficiencies of such effluent treatment.
Firstly, the effluent from MOCVD tools typically contains a large amount of hydrogen. The metal oxides in the dry scrubbing material can be reduced to metals by reaction with hydrogen, thus depleting the capacity of the dry scrubber for the hydrides. Such reduction reaction generally occurs at temperatures greater than room temperature, although the exact temperature necessary for such reaction to proceed depends on the metal oxide species in question.
Secondly, the reactions discussed hereinabove, wherein the metal oxide-containing dry scrubber reacts with hydrides, are exothermic in character. The heat generated by the hydride/metal oxide reaction is problematic as it can cause the reduction reaction between the metal oxides and hydrogen to become accelerated, thus depleting capacity.
Thirdly, in the use of the MOCVD process, it generally is strongly desired to increase the flow rates of hydrides to the processing tool, in order to effect high throughput operations. Such increase in hydrides, however, yields an increase in hydride concentration in the effluent of the tool, thus ultimately and undesirably increasing the heat formed during abatement.
Fourthly, an analysis of the reaction products of the above-described metal oxide/hydride reactions reveal that arsenic and phosphorus are formed. Phosphorus is particularly problematic as it can react upon exposure to air. If the reacted dry scrubbing media is not properly treated, a potentially hazardous situation may result.
In general, the problems associated with using dry scrubbing for the abatement of hydrides in the effluent of MOCVD processing can be generalized into the following categories: a) heat management problems, b) loss of treatment capacity of the scrubber material, necessitating remedial treatment to restore capacity lost due to metal oxide reduction, and c) the accumulation of hazardous materials in the dry scrubber bed, and the resultant necessity of treatment to remove hazardous materials from the dry scrubber bed.
It would therefore be a significant advance in the art to provide an abatement process that overcomes the aforementioned problems associated with the treatment of MOCVD process effluents and other gaseous effluents posing corresponding effluent treatment issues.
This invention relates to a process and apparatus for the treatment of effluents produced by metalorganic chemical vapor deposition (MOCVD).
The present invention relates in one aspect to an effluent abatement process for abating hydride species in a hydride-containing effluent, said process comprising (1) contacting the hydride-containing effluent with a dry scrubber material comprising a metal oxide that is reactive with the hydride species to substantially remove the hydride species from the effluent, until the capacity of the dry scrubber material for hydride species is at least partially exhausted, and (2) contacting the at least partially exhausted capacity dry scrubber material with an oxidant to at least partially regain the capacity of the dry scrubber material for the hydride species. Preferably the oxidant contacts the at least partially exhausted capacity dry scrubber material in the absence of contact with the hydride-containing effluent.
In another aspect, the invention relates to an effluent abatement system for abating hydride species in a hydride-containing effluent. Such process system comprises: a bed of dry scrubber material that is reactive with the hydride species in the hydride-containing effluent to remove the hydride species from the effluent; a source of the hydride-containing effluent joined in gas supply relationship to the bed of dry scrubber material; a source of an oxidant effective to regenerate the dry scrubber material subsequent to diminution of hydride removal capacity thereof, joined in oxidant supply relationship to the bed of dry scrubber material; and flow circuitry arranged to flow the hydride-containing effluent and the oxidant in contact with the bed of dry scrubber material. Preferably, the flow circuitry is arranged to repetitively and alternatingly flow the hydride-containing effluent and the oxidant in contact with the bed of dry scrubber material. Alternatively, the flow of oxidant and hydride-containing effluent may contact the dry scrubber material simultaneously.
Other objects, features and advantages of the invention will be more fully apparent from the ensuing disclosure and appended claims.